1. Field of the Invention
The present invention relates to an electronic circuit or subsystem and, more particularly, to an electronic oscillator that uses biasing voltages to maintain complementary metal oxide semiconductor (CMOS) transistors in a relatively low power consumptive state while achieving increased gain at higher frequencies of operation.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art or conventional by virtue of their inclusion within this section.
Within nearly every electronic subsystem is some form of generator that produces cyclical waveforms. The waveform generator is oftentimes referred to as an oscillator. Depending on the application, an oscillator can be used to source regularly spaced pulses or clock signals. Oscillators are oftentimes rated depending on their stability and accuracy, frequency adjustability (i.e., tunability), gain of active circuit, start-up time, power consumption, etc.
There are numerous types of oscillators in the marketplace. A simple form of oscillator is an RC relaxation oscillator. More complex and stable oscillators involve the more popular LC oscillator. While LC oscillators are more stable than RC oscillators, a crystal oscillator is generally more stable than LC oscillators.
Many crystal oscillators use some from of piezoelectric resonator, and take advantage of the piezoelectric effect of converting mechanical vibrations into electrical impulses (and vice-versa). The piezoelectric crystal material generally resides external from the integrated circuit used to apply alternating currents or voltages to the crystal. Therefore, the circuit initiates and amplifies the piezoelectric effect produced from a resonating crystal. The frequency produced from the circuit is governed by the resonant frequency of the crystal, and the resonant frequency (with harmonics) is governed by the crystal's equivalent electrical (motional) RM, LM, CM and shunt capacitor CS parameters. It is desirable for a good resonator to have a large quality factor (which depends on the ratio of LM/RM i.e. ratio of motional inductor to motion resistance).
There are many types of piezoelectric resonators. For example, instead of implementing a quartz crystal, the resonator can be formed on the integrated circuit along with the active circuitry used to initiate and amplify the piezoelectric effect. Such resonators are oftentimes referred to as surface acoustic wave (SAW) resonators. Both crystal resonators, such as quartz, gallium arsenide, LiNbO3, LiTaO3, or FBAR(ZnO), and SAW resonators are generally well-known.
Active circuitry amplifies small noise, present at the start-up, to produce a well behaved fixed amplitude sine wave whose frequency (=1/period) is governed by the resonator attached to the active circuitry. The time taken in this process, initial noise to generation of fixed amplitude sine wave, is known as the start-up time. The start-up time depends on the start-up gain provided by the active circuit, along with the resonator parameter, and tuning capacitor values. High start-up gain can reduce the start-up time (too high a gain is also not desirable, as defined by the circuit/resonator parameters the required gain is bounded by min and max values). Higher start-up gain leads to large power consumption at the start-up. It is desirable, however, to reduce active power. To this end some form of amplitude regulation can be used which reduces gain to min gain after start-up. It is also desirable for an oscillator to have low phase noise (low rms jitter). To be able to operate at high frequencies it is also desirable to obtain the maximum performance out of the devices. It is thus required that devices be biased in their maximum gain region. This optimum biasing can help achieve reduced parasitic from devices, further reducing the overall power consumption.